Effect of mercury on selenium binding to rat lens proteins in vitro.

The effect of mercury in the incubation medium on selenium influx, efflux and distribution was studied in eye lenses of 14-day-old rats. The presence of mercury did not affect the uptake of selenium into a water-soluble protein fraction but increased considerably its content in water-insoluble proteins and thus also the selenium influx into experimental lenses. The efflux from experimental lenses yielded significantly lower amounts of released selenium, most of the selenium being bound to proteins. In contrast, efflux experiments with control lenses showed most of the selenium to be in the medium in the form of free anions. The selenium content in experimental lenses decreased after the efflux only in the fraction of water-soluble proteins, while the decrease in control lenses was found in both fractions and was relatively higher in water-insoluble proteins. During both influx and efflux experiments the lenses of both groups released a small of proteins, but no difference found between the two groups.

Selenium metabolism in rats after administration of toxic doses of selenite.

We studied organ concentration, excretion and excreted forms of selenium in young and adult rats after a single s.c. injection of a sublethal dose of 75Se-selenite. In the young about a 10-fold higher concentration of 75Se in blood, liver, kidneys and In the young, about a 10-fold higher concentration of 75Se in blood, liver, kidneys and heart was found at all the experimental intervals studied (1-7 days). The highest 75Se concentration in the young was in the liver while in the adults it was found in the kidneys. The spectrum of radioselenium metabolites in the urine was the same in both groups. However, the main product excreted by young rats was 75Se-glutathione selenotrisulphide and an unidentified neutral substance while it was the trimethylselenonium ion in the adults. Ontogenetic differences in selenium metabolism could be one of the factors underlying the differences in the response of the young and the adult rats to toxic doses of selenite.

Age dependence of selenite uptake in rat eye lenses.

75Se-selenite was administered to young and adult rats in subcutaneous injection or added into the medium in which eye lenses were incubated. The 75Se uptake in lenses of the young was significantly higher in comparison with adults both in vivo and in vitro. The in vivo 75Se uptake, referred to unit of lens weight, was almost 500 times higher in young animals while in vitro it was only five times higher, which apparently reflects the age-dependent differences in the structure and function of membranes and/or system barriers.

Ontogenic changes in selenite metabolism in rats.

Radioselenium concentration and excretion was studied after administration of 75SE-labelled selenite to male rats during ontogeny. The concentration of radioselenium in individual organs decreases with increasing age. The largest differences between young and adults were in the quantity and quality of excreted substances. During 2 h after the administration of 20 mumol selenite/kg young rats excreted 2.4% of the dose, essentially in the urine only, whilst adults excreted a total of 11%, distributed equally in breath and urine. The part excreted as methylated metabolites was 0.1% of the administered dose in young and 6.3% in adult rats. These results support the hypothesis that the differences in the sensitivity to the toxic action of selenite between young and adult rats can be due to ontogenic differences in selenium metabolism.

The in vivo uptake of [3H]isoprenaline by the chick embryonic heart and liver.

Seven-day-old embryos received 3.7 x 10(5) Bq (10 muCi) of [3H]isoprenaline (IPRO) hydrochloride intraamnially. The capacity of myocardial and liver tissue for taking up administered catecholamine increased rapidly during the first 10 min after administration. The peak concentration (disintegrations per minute per milligram) in the heart, however, was significantly lower as compared with the liver. Thereafter the uptake in both organs markedly decreased and reached its lowest values between 15 and 30 min. From then on, the concentration of the tritium-labelled compound increased again and 6 h after administration it attained the second peak in both organs. This value was more than five times higher in the liver as compared with the myocardium. Radiometric evaluation of chromatograms from myocardial and liver extracts has revealed that IPRO is rapidly metabolized to 3-O-methyl IPRO. The proportion of this fraction in both organs represents approximately 40% of total radioactivity as early as 5 min after administration. The time course of IPRO uptake indicates that the following factors may participate in the development of cardiac and hepatic lesions: (a) IPRO immediately after administration, and (b) subsequently its toxic metabolites.

Radiation aggregates of insulin.

During the irradiation of aqueous solution of insulin (pH 1.8) the decrease of original insulin molecules and the formation of radiation aggregates of insulin was studied in dependence on the concentration of irradiation solution, on the doses and conditions of irradiation (oxygenated and oxygen-free atmosphere, the presence of t-butanol, addition of [14C]amino acids). From the results obtained and results published earlier it may be assumed that in irradiated solution on insulin new covalent bonds between insulin molecules are formed at tyrosyl, phenylalanyl and cystyl radicals; these radicals are formed by the action of both direct and indirect effect (at present pH 1.8 mainly of H atoms).

Gamma-radiolysis of aqueous solution of histidine.

The dependence of Gi(-M) values of histidine on the concentration of irradiated 10(-4) - 10(-1)M solutions, pH and the presence of O2, N2O and sec-butyl alcohol was investigated. In oxygen-free medium the maximum radiation sensitivity of histidine was found at pH 5--8; in oxygenated solutions it was shifted to the 6--1 pH range. The formation of radiation products was also studied. The course of radiation decomposition of histidine depends on the presence of oxygen and on the pH of irradiated solution.

Gamma-radiolysis of aqueous solution of proline.

Gamma-radiolysis of 0.05 M neutral proline solution was investigated. As the main reaction of proline radiolysis in oxygenated solutions, the hydroxylation reactions leading to hydroxyproline formation and the reactions leading to the total destruction of the pyrrolidine ring were shown. In oxygen-free solutions the yield of these reactions decreased; in this medium combination reactions giving rise to higher molecular weight combination products (up to approx. 1500) belong to the most important ones. In addition to radiation-decarboxylation reactions the products of radiation-carboxylation reactions were also detected in the irradiated solution of proline free of oxygen.